Camera Height vs Volume Width Study
Jereme Outerleys
2024-04-20
Study Overview
The objective of this study was to investigate the affect of camera height as a function of volume width on lower limb kinematics during normal walking using Theia3D. Video data was recorded for 9 subjects using 32 Sony RX0II cameras and processed in Theia3D (v2023.1.0.3161p9, model v10.0.0, 3DOF knee, 8 Hz cutoff frequency).
Camera Heights and Volume widths
Camera Heights
The 32 cameras were placed in a standard ellipse-like configuration (see
Figure 1). Cameras were placed at 4 heights for each
camera location:
- Group 1: 0.85m (hip height)
- Group 2: 1.65m (shoulder height)
- Group 3: 2.45m (HMRL standard setup)
- Group 4: 3.30m (HMRL scaffold/ceiling)
Group 0 included all 32 cameras during processing.
Volume Width
For each width the cameras were moved and re-aimed to get the subject in
all camera views as much as possible given the width constraints.
Width 1 was the standard HMRL volume length (~13.8m Long) and width. Width 2 and 3 were narrower. With width 3 trying to simulate hallway.
- Width 1: 6.9 m
- Width 2: 5.5 m
- Width 3: 3.3 m (not added yet)
A 5th and 6th group were added to Width 3 since the sagittal cameras for groups 1 and 2 could not get the full subjects. The sagittal cameras were replaced with videos from group 3.
Calibration
A single calibration was performed for each width with all 32 cameras.
Separate calibration files were then built by extracting the cameras for
each group
Data Processing
Only steps within a regional of interest were kept for analysis. The
region was defined to only include steps where the subject was visible
by all cameras. The same region was applied to each grouping to ensure
the same steps were used for analysis. The number of steps included
reduced as a function of width.
Ensemble average plots by camera height (group) and volume width.
Data only shown for Right Leg.
The plots are interactive:
- Click and drag to zoom.
- Hover over the line to see the group.
Draft interpretations per Jereme and Rob:
- Height doesn’t look to cause large differences, at least at these two widths (narrowest width still processing).
- The largest differences exist between the lowest and the highest heights as expected.
- The data when 36 cameras are included falls in between as expected, and biased towards the groupings that share similar views (Groups 2 and 3, i.e. shoulder height/above head height).
- There doesn’t seem to be a specific, consistent effect of width for any camera height.
- Lower cameras are generally less affected than higher ones. Areas during swing look most affected (distal limbs blocked by proximal limbs).
- For a balanced setup (i.e. all cameras or maybe just having cameras at multiple heights), there is almost no effect of width.
- Camera height adjusts the offset/starting point/average of the signals up or down, with low cameras having more ext. rot and high cameras having less.
- Looks like the leg axial rotation moves from being accounted for in the knee to the hip as the camera height increases. Results in opposite effects of height on those two joints.